Note: Descriptions are shown in the official language in which they were submitted.
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PROCESSES AND APPARATUS FOR REACTING
GASEOUS REACTANTS CONTAINING SOLID PARTICLES
Background of the Invention
1. Field of the Invention.
The present invention relates to processes and apparatus for reacting high
flow
rates of gaseous reactants containing particulate solids in tubular reactors,
and more
particularly, to reacting high flow rates of oxygen and titanium tetrachloride
gas which
can contain or pick up particulate solid contaminants in a tubular reactor at
high
temperature to produce titanium dioxide.
2. Description of the Prior Art.
In reactions carned out in tubular reactors where high flow rates of gaseous
reactants are injected into the reactors, problems with incomplete mixing and
severe
erosion of the side walls of the reactors due to the presence of particulate
solid
contaminants in the reactants can occur. The incomplete mixing can cause less
than
desirable reaction results and the erosion causes contamination of the
products produced
with the materials forming the reactors as well as drastically shortening the
lives of the
reactor apparatus. For example, in the production of titanium dioxide, the
gaseous
reactants are heated oxygen and heated titanium tetrachloride gas which are
combined in a
tubular reactor at high flow rates. A high temperature oxidation reaction
takes place in the
reactor whereby solid titanium dioxide particles are produced. Occasionally,
both the
oxygen and the titanium tetrachloride gas streams utilized in the reaction
contain or pick
up particulate solid contaminants which impinge on the surfaces of the reactor
apparatus.
Such particulate solid contaminants get into the gas streams as a result of
the passage of
the gas streams through process equipment and piping upstream of the reactor
apparatus.
The process equipment and piping can contain particulate solid scale, solid
particles from
fluidized beds, particulate welding slag and the like. Also, a particulate
solid scouring
medium such as sand is often introduced into the reactor apparatus to scour
titanium
dioxide deposited on the walls of the reactor therefrom. The scouring medium
occasionally finds its way into various upstream parts of the reactor
apparatus and some of
it is picked up and carned by the gaseous reactant streams. For example, if
the scouring
medium is being introduced into the reactor apparatus when the flow of oxygen
or
titanium tetrachloride is shut down, the scouring medium can flow out of the
reactor into
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oxygen or titanium tetrachloride introduction apparatus, e.g., plenum
chambers, connected
to the reactor.
In attempts to solve the problems mentioned above, large plenum chambers have
heretofore been utilized upstream of the reactor injection points of gaseous
reactants to
trap contaminants therein, and the gaseous reactants have been injected
through small
gaps. The use of small gaps results in high pressure drops which bring about
good mixing
of gases in the reactor, but the high pressure drops in the gaseous reactants
require their
pressurization which is very costly.
In order to operate with lower gaseous reactant pressure drops, the gaseous
reactants have heretofore been tangentially injected into small annular plenum
chambers
which distribute them around two or more slots through which the gaseous
reactants flow
radially into the reactor. The use of injection through the slots brings about
low pressure
drops, but particulate solid contaminants carned or picked up by the gaseous
reactants can
be trapped in the annular plenum chambers which causes the plenum chambers to
be
rapidly eroded.
Thus, there are needs for improved processes and apparatus for reacting
gaseous
reactants in tubular reactors which bring about low pressure drops across the
reactor
apparatus, more uniform distribution of the gaseous reactants and better
mixing of the
gaseous reactants without excessive erosion due to the presence of solid
particles.
Summary of the Invention
The present invention provides improved processes and apparatus for reacting
solid particle containing gaseous reactants in tubular reactors which meet the
needs
described above and overcome the deficiencies of the prior art.
A process of the present invention for reacting a high flow rate of a gaseous
reactant which can contain or pick up solid particles in a tubular reactor is
comprised of
the following steps. The gaseous reactant to be injected is swirled in a first
annular
plenum chamber followed by a second larger diameter annular plenum chamber.
The
swirling gaseous reactant is then introduced into the reactor by way of two or
more radial
slots communicating the reactor with the outlet of the second plenum chamber
whereby
solid particles carried with the gaseous reactant are caused to flow into the
reactor with the
gaseous reactant and are not trapped in the first or second plenum chambers.
The radial
slots bring about the uniform distribution and alignment of the flow of the
gaseous
reactants and solid particles through the center of the reactor and thereby
prevent
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incomplete mixing and erosion therein. In the production of titanium dioxide,
the above
described process is preferably utilized for injecting high flow rates of
heated oxygen into
the reactor.
Another process of this invention which can also be utilized for introducing a
high
flow rate of a gaseous reactant into a tubular reactor which meets the above
described
needs is as follows. The high flow rate gaseous reactant which can contain
solid particles
is swirled in an annular plenum chamber which includes a boot formed therein
for
catching the solid particles. The resulting substantially solid particle free
gaseous reactant
is introduced into the reactor by way of two or more radial slots
communicating the
reactor with the plenum chamber. A conduit is optionally provided in the
plenum
chamber extending from the interior of the boot to within one of the annular
slots whereby
the gas pressure differential between the boot and the slot causes the solid
particles caught
in the boot to be swept through the conduit into the reactor. The radial slots
are preferably
slanted in the downstream direction to facilitate the uniform distribution and
alignment of
the flow of the gaseous reactant and solid particles {if any) through the
center of the
reactor and thereby prevent incomplete mixing and erosion therein. In the
production of
titanium dioxide, this process is preferably utilized for injecting high flow
rates of heated
titanium tetrachloride into the reactor.
Apparatus for carrying out the above described processes are also provided by
the
present invention.
It is, therefore, a general object of the present invention to provide
improved
processes and apparatus for reacting solid particle containing gaseous
reactants in tubular
reactors.
A further object of the present invention is the provision of improved
processes
and apparatus for reacting high flow rates of oxygen and titanium
tetrachloride gas which
may contain or pick up particulate solid contaminants in a reactor for
producing titanium
dioxide.
Other and further objects, features and advantages of the present invention
will be
readily apparent to those skilled in the art upon a reading of the description
of preferred
embodiments which follows when taken in conjunction with the accompanying
drawings.
Brief Description of the Drawings
FIGURE 1 is a top view of the solid particle containing gaseous reactant
injection
apparatus of this invention connected to a tubular reactor.
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FIGURE 2 is a side cross-sectional view taken along line 2-2 of FIG. 1.
FIGURE 3 is a cross-sectional view taken along line 3-3 of FIG. 2.
FIGURE 4 is a cross-sectional view taken along line 4-4 of FIG. 1.
FIGURE 5 is a side cross-sectional view taken along line S-5 of FIG. 1.
FIGURE 6 is a cross-sectional view taken along line 6-6 of FIG. 5.
FIGURE 7 is a cross-sectional view taken along line 7-7 of FIG. 5.
Description of Preferred Embodiments
Referring now to FIGS. 1 through 6 of the drawings, the apparatus of the
present
invention for injecting high flow rates of gaseous reactants containing solid
particles into a
tubular reactor is illustrated. The term "high flow rates" is used herein to
mean flow rates
in the range of from about 400 to about 3,000 or higher standard cubic feet
per minute.
In FIG. 1, the apparatus of this invention is illustrated in combination with
a
tubular reactor for producing titanium dioxide from heated oxygen and heated
titanium
tetrachloride gas streams which can contain or pick up particulate solid
contaminants and
which are injected at high flow rates into the tubular reactor. The tubular
reactor can be of
any known reactor design including those that are cooled with water or other
heat
exchange medium, those which are not cooled, those that are formed of a porous
medium,
etc.
The apparatus of FIG. 1, generally designated by the numeral 10, is comprised
of a
first form of gaseous reactant introduction apparatus 12 and a second form of
gaseous
reactant introduction apparatus 14, both for introducing high flow rates of
gaseous
reactants which may contain solid particles into the tubular reactor 19. The
apparatus 12
a,nd 14 can each be utilized for injecting any high flow rate gaseous reactant
which does or
may contain solid particles into a tubular reactor. In apparatus for producing
titanium
dioxide, the gaseous reactant introduction apparatus 12 and 14 can be utilized
for
introducing either the heated oxygen or the heated titanium tetrachloride gas
streams into
the titanium dioxide production reactor 19. However, the gaseous reactant
introduction
apparatus 12 shown in FIGS. 1-4 is preferred for introducing the heated oxygen
stream
into the reactor 19. The gaseous reactant introduction apparatus 14 shown in
FIGS. 1 and
5-7 is preferred for introducing the heated titanium tetrachloride gas stream
which is
highly corrosive into the reactor 19.
In operation, both the apparatus 12 and the apparatus 14 introduce high flow
rates
of gaseous reactants which may contain solid particles into the tubular
reactor 19 with low
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pressure drops, with uniform distribution and good mixing of the gaseous
reactant streams
in the reactor and without excessive plenum chamber or reactor erosion due to
the
presence of solid particles canned with the gaseous reactants.
As shown in FIGS. 1-4, the apparatus 12 is comprised of a cylindrical gaseous
reactant injection chamber 16 having an annular opening 17 around the
periphery thereof
and flange connections 18 and 20 connected to the forward and rearward ends 19
and 21
thereof; respectively. A closing flange 22 is attached to the flange 18. A
conduit 24 is
sealingly connected through the flange 22 and extends into the cylindrical
injection
chamber 16. The conduit 24 is positioned coaxially with the cylindrical
injection chamber
16 and a second conduit 26 which is also sealingly connected through the
flange 22 is
coaxially disposed around the conduit 24. An inlet flange 28 is connected to
the conduit
24 and a flanged inlet connection 30 is connected to the conduit 26. As
indicated in FIG.
1, when the gaseous reactant introduction apparatus 12 is utilized with a
water cooled
titanium dioxide production reactor, a source of auxiliary fuel, e.g.,
methane, propane or
toluene, is connected to the inlet connection 30 of the conduit 26, and a
source of reactor
scouring medium is connected to the inlet connection 28 of the conduit 24. The
auxiliary
fuel is utilized to provide additional heat and to stabilize the oxidization
reaction in the
reactor 19. The fuel is oxidized to carbon dioxide and water and the water
formed
promotes rutilization which improves the properties of the titanium dioxide
produced.
The reactor scouring medium which can be sand, rock salt, sintered titanium
dioxide,
compressed titanium dioxide or the like is injected into the reactor apparatus
to scour
titanium dioxide from the cooled walls of the reactor. As the titanium dioxide
is formed in
the reactor, some of it deposits on the walls of the cooled portions of the
reactor, e.g., the
part of the reactor cooled by water or other means. Unless removed, the
titanium dioxide
will continuously build up and substantially interfere with the cooling
process. Thus, the
scouring medium must be continuously introduced into the reactor.
The injection chamber 16 also includes a pair of cooling water jackets 32 and
34
for cooling the walls of the injection chamber. In addition, an annular heat
shield 35 is
disposed within the cylindrical gaseous reactant injection chamber 16 between
the annular
opening 17 in the injection chamber and the forward end 19 thereof. The heat
shield 35
can be welded to the conduit 26 and it functions to shield the forward end
portion of the
cylindrical gaseous reactant injection chamber 16 from the heat produced by
the heated
gaseous reactant (heated oxygen) introduced through the annular opening 17
thereof.
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Also, as will be described further hereinbelow, a deflector 37 for deflecting
the flow of the
heated oxygen introduced into the injection chamber 16 by way of the opening
17 and
causing it to be uniformly distributed is attached to the rearward end portion
39 of the
conduit 26.
A first annular plenum chamber 36 is provided having an annular outside wall
38,
a side 40 sealingly attached to the exterior of the gaseous reactant injection
chamber 16
and an annular side outlet 42. As best shown in FIG. 4, the first annular
plenum chamber
36 also includes a tangential inlet 44 for receiving a high flow rate stream
of heated
oxygen which may contain solid particles and causing the stream to swirl
within the
plenum chamber 36.
A second annular plenum chamber 46 having an annular outside wall 47 and sides
48 and 50 is also sealingly attached to the exterior of the injection chamber
16. The side
50 of the second plenum chamber 46 is attached to the outside wall 38 of the
first plenum
chamber 36 and the second plenum chamber 46 includes an annular side inlet 52
which
coincides with the annular side outlet 42 of the first plenum chamber 36. As
shown in the
drawings, the second plenum chamber 46 has a larger diameter than the first
plenum
chamber 36 and the second plenum chamber 46 covers the annular opening 17
around the
periphery ofthe injection chamber 16.
An annular slot 54 is formed within the second plenum chamber 46 adjacent to
the
side 48 thereof by an annular plate 56 which is sealingly attached to the
exterior of the
injection chamber 16 and extends to near the outside wall 47 of the second
plenum
chamber 46. The annular slot 54 formed by the side 48 of the second plenum
chamber 46
and the annular plate 56 is sealingly attached over the annular opening 17 in
the injection
chamber 16. Thus, as will be described in greater detail hereinbelow, the high
flow rate of
heated oxygen which may contain solid particles conducted to the tangential
inlet 44 of
the first plenum chamber 36 is caused to swirl within the first plenum chamber
36
followed by swirling in the larger second plenum chamber 46 and flowing out of
the
second plenum chamber 46 by way of the annular slot 54 into the interior of
the injection
chamber 16. Because the heated oxygen stream is first swirled within the
smaller plenum
chamber 36 and then expanded and swirled in the plenum chamber 46, solid
particles
contained in the stream are moved by centrifugal force to the outside walls 38
and 47 of
the plenum chambers 36 and 46 from where the solid particles are caused to
flow along
with the heated oxygen through the slot 54 into the interior of the injection
chamber 16
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and the solid particles are not trapped within the plenum chambers 36 and 46.
As is well
understood by those skilled in the art, when solid particles are trapped
within a plenum
chamber in which a high velocity gas stream is swirled, the solid particles
erode and cut
through the material forming the plenum chamber in a very short period of
time. As
shown best in FIG. 2, the outside wall 47 of the plenum chamber 46 is sloped
outwardly
towards the side 48 thereof to facilitate the movement of the solid particles
into the slot
54.
As best shown in FIG. 3, the annular slot 54 includes a plurality of spaced
vanes
58 attached therein which form a plurality of radial slots 59 (FIG. 3) in the
opening 54.
The radial slots 59 function to stop the heated oxygen stream from swirling
and uniformly
distribute the flow of the heated oxygen stream and solid particles carned
therewith into
and through the center of the injection chamber 16. The deflector 37 attached
to the
interior end portion 39 of the conduit 26 functions to cause the heated oxygen
stream to be
uniformly distributed and to uniformly flow through the center of the
injection chamber
16, the titanium tetrachloride gas introduction apparatus 14 and the reactor
19 thereby
preventing incomplete mixing and erosion from taking place.
Thus, the process carried out in the apparatus 12 basically comprises the
steps of
swirling the gaseous reactant to be introduced into the reactor 19 in the
first annular
plenum chamber 36 followed by the second larger diameter annular plenum
chamber 46.
The swirling gaseous reactant and solid particles carried therewith are
introduced into the
reactor 19 by way of the radial slots 59 and the injection chamber 16. That
is, the gaseous
reactant and solid particles flow through the radial slots 59 into the
injection chamber 16
and then into the reactor 19 and the solid particles are not trapped in the
first or second
plenum chambers. The radial slots 59 and the deflector 37 disposed within the
injection
chamber 16 cause the gaseous reactant and solid particles to flow into and
through the
injection chamber 16 in a manner whereby the gaseous reactant and solid
particles
uniformly flow through the centers of the injection chamber 16 and reactor 19
thereby
preventing incomplete mixing and erosion therein. As mentioned, when the
apparatus 12
is utilized in a process for producing titanium dioxide, the gaseous reactant
introduced into
the reactor 19 by way of the apparatus 12 is preheated oxygen, i. e., oxygen
preheated to a
temperature in the range of from about 1000°F to about 1800°F,
preferably from about
1500°F to about 1800°F. In addition, an auxiliary fuel is
preferably introduced into the
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injection chamber 16 and reactor 19 by way of the conduit 26, and a scouring
medium for
scouring the walls of the reactor are introduced into the injection chamber 16
and reactor
19 by way of the conduit 24. Also, potassium chloride, cesium chloride or the
like can be
added to the heated oxygen introduced into the reactor 19 to control the
particle size of the
titanium dioxide produced.
Referring now to FIGS. l and 5-7, the apparatus 14 for introducing a high flow
rate of a gaseous reactant (heated titanium tetrachloride) which contains or
may contain
solid particles into the reactor 19 is illustrated. As best shown in FIG. 5,
the apparatus 14
includes a cylindrical gaseous reactant injection chamber 60 having a forward
end 61 and
a rearward end 65 adapted to be sealingly connected to the upstream end of the
tubular
reactor 19 by way of a conical connecting pipe section 23 (FIG. 1) and having
an annular
opening 69 formed therein around the periphery thereof. As will be understood
by those
skilled in the art, the apparatus 14 can be formed of various materials which
have desired
insulating, corrosion resistant and other properties. In the form illustrated
in the drawings
for use in apparatus for producing titanium dioxide, the injection chamber 60
is comprised
of a cylindrical wall member 63 formed of a heat insulating refractory
material, a
cylindrical member 64 formed of corrosion resistant metal material and a
cylindrical
member 66 formed of a corrosion resistant silicon carbide material. The
annular opening
69 is preferably angled towards the rearward end 65 of the injection chamber
60 as shown
in FIG. 5, and the annular opening 69 includes a plurality of spaced vanes 68
(FIG. 6)
disposed therein which form a plurality of radial slots 62 therein. The radial
slots 62 and
annular opening 69 are angled in order to prevent oxygen from entering them,
the build up
of oxides in the slots which can lead to plugging and to facilitate uniform
distribution in
the injection chamber 60. The vanes 68 can be integrally formed in the
cylindrical
member 66 as shown in the drawings. Also, when auxiliary fuel is utilized for
providing
additional heat as described above, the cylindrical wall member 63, the pipe
section 67,
the conical connecting pipe section 23 (FIG. 1) and the reactor 19 (FIG. 1)
are all water
cooled (not shown) to prevent damage thereto as a result of the high
temperatures
involved.
An annular plenum chamber 70 having an outside wall 72 and sides 74 and 76
formed of a metal such as steel is sealingly attached to the exterior of the
cylindrical
gaseous reactant injection chamber 60. The interior of the annular plenum
chamber 70 is
lined with a silicon carbide corrosion resistant material 78 and a gasket
material 80 is
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disposed between the corrosion resistant material 78 and the outside wall 72
and sides 74
and 76. As will be understood, insulating and corrosion resistant materials or
techniques
other than those described above can be utilized in the apparatus 14.
As best shown in FIG. 7, a tangential inlet 82 for receiving a high flow rate
stream
of heated titanium tetrachloride gas which contains or may contain solid
particles is
attached to the plenum chamber 70. The tangential inlet 82 causes the titanium
tetrachloride gas stream to swirl within the plenum chamber 70. A tangential
boot 84 is
formed in the plenum chamber 70 downstream from the tangential inlet 82
thereof for
catching solid particles carried with the titanium tetrachloride gas stream.
The boot 84
includes a removable blind flange 85 bolted thereto for periodically removing
solid
particles therefrom. Thus, as will be described further hereinbelow, the
titanium
tetrachloride gas stream containing solid particles is swirled within the
plenum chamber
70, the solid particles are caught in the boot 84 and the resulting
substantially solid particle
free titanium tetrachloride stream flows into the injection chamber 60 by way
of the radial
slots 62 and opening 69.
As best shown in FIG. 7, a conduit 86 can optionally be attached within the
plenum chamber 70 which has one end 88 extending into the boot 84 and the
other end 90
extending into a radial slot 62. The gas pressure differential between the
boot 84 and the
radial slot 62 causes solid particles caught in the boot 84 to be swept along
with a portion
of the titanium tetrachloride gas stream through the conduit 86 into the
injection chamber
60 and the reactor 19.
The spaced vanes 68 disposed in the annular slot 69 which form the radial
slots 62
cause the titanium tetrachloride gas stream to slow or stop swirling and to be
uniformly
distributed in the injection chamber 60 in a manner such that the gas stream
and solid
particles (if any) flow through the center of the injection chamber 60 and
reactor 19
thereby preventing incomplete mixing and erosion therein.
Thus, the process carried out in the apparatus 14 basically comprises swirling
the
gaseous reactant that may contain or pick up solid particles in the annular
plenum chamber
70 which includes a boot 84 formed therein for catching the solid particles.
The resulting
substantially solid particle free swirling gaseous reactant flows into the
injection chamber
60 by way of the radial slots 62 and annular opening 69. The solid particles
caught in the
boot 84 can be manually withdrawn therefrom periodically or they can be
withdrawn
continuously by the conduit 86 and caused to flow into a slot 62. As mentioned
above, the
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plurality of radial slots 62 function to cause the gaseous reactant and solid
particles (if
any) to be uniformly distributed in the injection chamber 60 and align the
flow of the
gaseous reactant and solid particles through the center ofthe injection
chamber 60.
As also mentioned, when the apparatus 14 is utilized in a process for
producing
titanium dioxide, the gaseous reactant introduced into the reactor 19 by the
apparatus 14 is
titanium tetrachloride gas, i.e., titanium tetrachloride gas preheated to a
temperature in the
range of from about 350°F to about 1800°F, preferably from about
750°F to about
1100°F. As will be understood, aluminum chloride can be added to the
heated titanium
tetrachloride to enhance rutilization of the produced titanium dioxide and
make it more
durable.
The process of the present invention carried out in the apparatus 10 shown in
FIG.
1 for producing titanium dioxide by reacting high flow rates of oxygen and
titanium
tetrachloride gases in the tubular reactor 19 is generally carried out at a
pressure of at least
about 2 psig and a temperature of at least about 2200°F. Also, the
temperatures of the
oxygen and titanium tetrachloride streams are controlled so that the
temperature of the
composite stream before reaction is in the range of from about 900°F to
about 1800°F,
preferably about 1450°F. The process carried out in the apparatus 10
basically comprises
the steps of swirling heated oxygen which contains or may contain solid
particles in the
first annular plenum chamber 36 followed by the second larger diameter annular
plenum
chamber 46. The swirling oxygen is introduced into the reactor 19 by way of
the oxygen
injection chamber 16 through a first set of radial slots 59 communicating the
injection
chamber 16 with the outlet of the second plenum chamber 46 whereby solid
particles
contained therein are caused to flow into the injection chamber with the
oxygen and are
not trapped in the first or second plenum chambers. The radial slots 59 are
formed by a
plurality of spaced vanes 58 disposed in the annular opening 54. The radial
slots 59
uniformly distribute and facilitate the alignment of the flow of the oxygen
and solid
particles carried therewith through the centers of the oxygen injection
chamber 16, the
titanium tetrachloride injection chamber 60 and the reactor 19 and thereby
prevent
incomplete mixing and erosion therein. The deflector 21 also functions to
align the flow
ofthe heated oxygen and mix the combustion products.
The titanium tetrachloride gas which contains or may contain solid particles
is
swirled in the third annular plenum chamber 70 which includes a boot 84 formed
therein
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for catching the solid particles. The resulting substantially solid particle
free swirling
titanium tetrachloride gas is introduced into the injection chamber 60 and
into the reactor
19 by way of a second set of radial slots 62 communicating the injection
chamber 60 with
the plenum chamber 70. A conduit 86 is optionally provided in the plenum
chamber 70
extending from the interior of the boot 84 to within a slot 62 whereby the gas
pressure
differential between the boot 84 and the slot 62 causes the solid particles
caught in the
boot to be swept through the conduit into the injection chamber 60 and the
reactor 19.
The spaced vanes 68 disposed in the annular opening 69 form the slots 62 which
cause the
titanium tetrachloride gas to be uniformly distributed in the injection
chamber 60 and align
the flow of the titanium tetrachloride gas and solid particles carned
therewith (if any)
through the center of the injection chamber 60 and the reactor 19 thereby
preventing
incomplete mixing and erosion therein.
As will now be understood by those skilled in the art, the improved processes
and
apparatus of the present invention for reacting gaseous reactants containing
solid particles
at high flow rates in tubular reactors make it possible to carry out the
reactions at low
pressure drops with uniform distribution and better mixing of gases in the
reactors without
excessive erosion. As will also be understood by those skilled in the art, the
improved
processes and apparatus of the present invention can be utilized for reacting
a variety of
reactants containing solid particles at high flow rates and temperatures. The
processes and
apparatus are particularly suitable for reacting preheated oxygen and
preheated titanium
tetra- chloride containing solid particles in tubular reactors for producing
titanium dioxide.
In addition, they are suitable for reacting preheated oxygen with other
preheated metal
chlorides such as silicon tetrachloride, zirconium tetrachloride, aluminum
tetrachloride
and the like.
Thus, the present invention is well adapted to carry out the objects and
attain the
ends and advantages mentioned as well as those which are inherent therein.
While
numerous changes may be made by those skilled in the art, such changes are
encompassed
within the spirit of this invention as defined by the appended claims.
What is claimed is:
